Nobody special needed Geoff, but do check the small print - pre-existing conditions are often excluded. However it does not mean they WON'T cover them if you ask them.
We get our travel cover nominally 'free' with our bank account. I have to declare my diabetes annually! (I always confuse the person I speak to by asking Why do I have to do this annually? Please explain how I might not still have it one year?) But they don't charge me any extra for it.
In fact I have never ever been charged extra for D on any insurance cover. Other things yes, but D, no. And I've never gone with a 'specialist' insurer for anything, just whoever.